Where in the portable manual did you find about fadec? I can't find it anywhere...
I fly a DA40 in Germany with fadec, and never had any issues with my powerflarm, even though I have the powerflarm core. I have one top and one bottom antenna (the AV-75 flarm antennas) and receive other aircraft with flarm well over 10 km away. If you have problems, it's most probably with your antenna installation.
Flarm has saved me twice in the last three years, last time this summer when I was seconds from colliding with a helicopter. Luckily he also had flarm (in Germany, almost all helicopters have flarm).